Transport and dispersion patterns of aerosols over the east African region
Abstract
This study used aerosol optical depth (AOD) from satellite
based Moderate Resolution Imaging Spectroradiometer
(MODIS) observations at 550nm in 1° X 1° grid resolution to
investigate the transport and dispersion patterns of aerosols
over the East African region. The specific objectives of the
study was to perform spatial analysis using monthly means of
MODIS Terra AOD data, evaluate monthly means for a five
year MODIS Terra AOD data, examine diurnal patterns
between MODIS Terra and MODIS Aqua AOD data, and
simulate transport and dispersion of the AOD during the North
Easterly Trade winds and the South Easterly Trade winds to
identify the possible sources and sinks of the aerosols. The
region of study lies within 28.5°E-42.5°E, 4.5°N-12.5°S.
Several analyses were performed. To begin with, time series
analysis was performed on the data which revealed the
seasonality and a bimodal annual pattern of the MODIS Terra
AOD data. The Hovrnoller analysis revealed spatial and
temporal patterns of the aerosols hence clearly showing
areas of higher AOD values in space and time; an indication
of high aerosol concentrations.
Backward air trajectory analysis was performed to identify the
possible sources of aerosols for a period of forty eight (48 hrs)
hours of air transport over three selected locations namely:
2°S, 300E; 2°S, 400E and 4°N, 36°E. These three locations had
indicated higher AOD values by performing spatial and
Hovmoller analysis. High AOD values symbolize high aerosol
concentrations. Through backward air trajectory analysis, the
possible sources of aerosols in the Northern hemisphere were
found to be the Middle East, Sahara and Arabian deserts
during the month of February, whereas in the Southern
hemisphere, the possible sources were found to be the
Congo rain forest, Kalahari and Namibian deserts, Southern
Atlantic Ocean, South west Indian Ocean, Madagascar
Island and South African region during the month of July.
Also, computed was the forward air trajectory analysis over
the same locations. These were necessary in identifying
whether there were possible transport and dispersion of
aerosols within the region of study. Through the forward air
trajectory analysis, it was discovered that aerosols are greatly
dispersed over the Eastern African region. This dispersion is
depended on the prevailing wind flow patterns.
The findings of this study established that long distance
transport of aerosols and their dispersion through low level
winds is responsible for the aerosols affecting the East African
region. The transport of aerosols and their dispersion patterns
greatly depend on the season of the year together with the
prevailing atmospheric conditions
Citation
Master of Science (MSc) in MeteorologySponsorhip
University of NairobiPublisher
Department of Meteorology University of Nairobi